1. Field of the Invention
The present invention relates to an electron source provided with wirings and electron emitting portions, and a producing method therefor.
2. Related Background Art
The electron emitting device is conventionally known in two types, namely a hot electron source and a cold cathode electron source. Within the cold cathode electron source, there are known, for example, an electric field emission type (hereinafter represented as EF), a metal/insulating layer/metal type (hereinafter represented as MIM), a surface conduction electron emitting device etc.
The element of EF type is disclosed for example by W. P. Dyke & W. W. Dolan, “Field emission”, Advance in Electron Physics, 8, 89 (1956).
The element of MIM type is disclosed for example by C. A. Mead, “Tunnel-emission amplifier”, J. Appl. Phys., 32, 646 (1961).
The surface conduction electron emitting device is disclosed for example by M. I. Elinson, Radio Eng. Electron Phys., 10 (1965).
The surface conduction electron emitting device utilizes a phenomenon of electron emission by causing, in a thin film of a small area formed on a substrate, an electric current parallel to the plane of the film. Such surface conduction electron emitting device is reported in various types such as one utilizing a thin SnO2 film reported by Elinson mentioned above and others, one utilizing a thin Au film (G. Dittmer: “Thin Solid Films”, 9, 317 (1972)), one utilizing an thin In2O3/SnO2 film (M. Hartwell and C. G. Fonstad: “IEEE Trans. ED. Conf.”, 519 (1975)) and one utilizing a thin carbon film (H. Araki et al., Shinkuu, 26, Vol. 1, p.22 (1983)).
As a representative device configuration of such surface conduction electron emitting devices, FIG. 14 shows the configuration of the device reported in the aforementioned reference of M. Hartwell. In FIG. 14, there are shown an insulating substrate 901, and a thin film 902 for forming an electron emitting portion, composed for example of an H-shaped metal oxide formed by sputtering and adapted to form an electron emitting portion 905 by a current-passing process, which is called forming as will be explained later.
In such surface conduction electron emitting device, an electron emitting portion 905 is generally formed by subjecting in advance the thin film 902 for forming the electron emitting portion, prior to the electron emission, to a current passing process which is called forming. More specifically, the forming process consists of applying a voltage across the ends of the thin film 902 for forming the electron emitting portion thereby locally destructing, deforming or denaturing such thin film to form the electron emitting portion 905 of an electrically high resistance state. The electron emitting portion 905 may be composed of fissures generated in a part of the thin film 902 for forming the electron emitting portion and may cause electron emission from the vicinity of such fissures.
The above-described cold cathode electron source, particularly the surface conduction electron emitting device, provides an advantage that a multitude of devices can be arranged over a large area because of its simple structure and easy manufacture. For this reason, there are being investigated various applications allowing to exploit such advantage. Examples of such applications include an electron source substrate (charged beam source) consisting of an array of plural electron emitting devices, and an image forming apparatus such as a display apparatus utilizing such electron source substrate.
A configuration of the electron source substrate consisting of an array of plural electron emitting devices has a simple matrix wiring including plural first conductor layers, plural second conductor layers crossing the plural first conductor layers, and plural electron emitting devices positioned at the respective crossing points of both conductor layers and connected to such both conductor layers.
FIG. 12 shows the configuration of a conventional electron source substrate in which the surface conduction electron emitting devices, constituting cold cathode electron emitting devices, are wired in a simple matrix (in which the second conductor layer is illustrated in a partially cut-off state), and FIGS. 13A to 13E show steps of the manufacturing process for the electron source substrate. In FIGS. 12 and 13A to 13E there is only shown the vicinity of a crossing portion of both conductor layers.
Referring to FIGS. 12 and 13A to 13E, there are shown a surface conduction electron emitting device 101, device electrodes 102, 103, a thin film 104 for forming an electron emitting portion, a first conductor layer 105, an interlayer insulation layer 106, a void pattern (contact hole) 107 provided in the interlayer insulation layer, and a second conductor layer 108.
In the connecting portion of the device electrode 102 and the second conductor layer 108, the second conductor layer 108 tends to become considerably thick since it is formed in a form sinking into the void pattern 107 provided in the interlayer insulation layer 106. Also the conductor layers tend to become thicker in realizing the matrix wiring of a low resistance.
Since the second conductor layer 108 is in general formed with a thick film material, there is generated a large thermal stress to eventually result in a phenomenon in which the device electrode 102, connected to the second conductor layer 108 and having different lengths at the left and right portions, is fissured in the longer portion by the thermal stress of the above-mentioned thick film, thereby significantly deteriorating the electrical connectivity in such portion.